Case-hardening metals



Patented Mar. 27, 1934 UNl'l-ED T PATENT-ferries ama ' oAsE-nARnENmG METALS Ernest C. Moffett, Woodbridge, N. J.,, assignor to' American Cyanamid'Company, New York, N. Y.,

a corporation ofMaine No-Drawin'g. Application July 11, 1931, j

'Serial Nth-550,287 l 8 Claims. (Cl, '148- -15) v This invention relates to case-hardening of- With a bath containing 40% sodium cyanide and metals and is more particularly directed to a the balance consisting of sodium carbonate and composition forming a molten bath in'whi'ch' sodium chloride also maintained at 1525" F., simmetals are immersed forthe purpose of hardenilar low carbon steel was ,given a case of 0.005 ing the surfacethereof. inch intwenty-five minutesp Similar superior 60 Sodium cyanide has frequently been used, results are obtainedat'difierent times and temeither alone, or mixed with sodium chloride and" peratures using various grades of steel. sodium carbonate for case-hardening steel. The The sodium-cyanide used may be the ordinary depth of case, the hardness, etc. obtainable by the commercial grade containing 96% to 98% pure 10 use of such mixtures are well-known. However, sodium cyanide, although other-grades may be 65 it is further known that efficient case-hardening used in place thereof. I may prepare a special does not take place with such materials unless a mixture by the fusion of sodium cyanide with calrelatively high concentration of sodium cyanide cium chloride and sodium chloride in such prois used and maintained. Thus. the usual caseportions as to maintain the desired ratio of the hardening bath for steel contains at least 25% three constituents of the bath. The fused mateof sodium cyanide and preferably higher perrials may be cooled and cast in the form of blocks centages. The molten bath of the usual type convenient to handle, or may be prepared in any containing sodium cyanide has many other disother suitable form. advantages and limitations. While many theories and explanations may I have discovered that it is possible to casesuggest themselves to those skilled in the art 75 harden steels and like metals in a sodium cyanide to account for the improved results obtained by bath without the disadvantages of the prior art me, it would appear that the superiority of my methods and compositions. By my invention I bath may be explainedas follows. Sodium cyam able to produce a deeper case in less time than anide decomposes in the usual case-hardeningwas heretofore possible with baths of this charbath and forms sodium carbonate and carbon 80 acter. This is done by using a molten bath conmonoxide. the latter serving to carburize the surtaining very small percentages of sodium cyanide face of the steel. However, sodium carbonate deand including a mixture of alkali metal and alkali carburizes steel and a point is reached where the earth metal halides, the latter in preponderance. tendency for the sodium carbonate to remove car- The following specific example is given as an bon from the steel exceeds the rate at which illust at of y invention Without in a y Way sodium cyanide adds carbon thereto. This equiserving as a limitation thereof. The composition librium can only be Overcome by t of high which is molten to serve as a case-hardening bath concentrations of sodium cyanide in the bath comp a mixture of an alkali metal halide. an with the obvious disadvantages of such an ineffi- 35 alkali earth metal halide, and a small amount i t procedure a 9 of sodium cyanide, t e alkali earth metal halide In my bath, such sodium carbonate as may be being present in p p ce. MO p formed can be removed from the bath or is pres y. I make a mixture Containing One p y vented from decarburizing the steel by the use 01' wei t f sodium chloride and two parts the alkali earth metal halide such as calcium Weight of calcium P i mixture is dliled chloride. These latter compounds form insoluble and is readyfor 1n the meltmg P the f" alkali earth metal carbonates or oxides according After mlxture 1S molten there 13 added sodl' to the temperature of operation, and the carbon um cyamde m the amount of 1/2 to 1% of the total ate or oxide is either dissolved in the exe ass alkali bath. With a bath consisting of 100 lbs. of the 1 earth metal halide or if some of it fails to dissolve, 100 mixed chlorides, I add /2 to 1 1b. of sodlum it will be m d to sink to the bottom of the cyanide. The bath is operated in the usual man-.

a molten bath as a sludge and can be removed by ner and, in accordance with the usual practice, means of a la dle or the like. of course, it is th sodium 0 anide isre laced as it is consumed. lneordinary osgerationy I E about 1/ to 1% sodi understood that I do not wlsh to restrict myself 50 um cyanide per 1101113 Likewise, the efficacy of to this theory of operation, although it would the bath can be maintained by the addition of appear to account for the marked efiiclency and suitable quantities of the chlorides, as necessary. Superiority of my bath.

With the bath just described, maintained at a It w ll be pp that many h n s and vatemperature of 1525 F., a case of 0.007 inch was riations other than those described can be made produced on low carbon steel in fifteen minutes. in the composition of the bath, as well as in the metal chloride, the alkali earth metal chloride forming at least 50% of the mixture.

2. A molten bath for case-hardening metals. comprising essentially not substantially over 1% of sodium cyanide and a mixture of salts including an alkali earth metal chloride and an alkali metal chloride in the proportion of two parts alkali earth metal halide to one part alkali metal chloride.

3. A molten bath for case-hardening metals comprising essentially to 1% sodium cyanide and a mixture of salts including an alkali earth metal chloride and an alkali metal chloride, the alkali earth metal chloride forming at least 50% of the mixture.

4. A molten bathfor case-hardening metals comprising essentially A to 1% sodium cyanide and a mixture of salts including an alkali earth metal chloride and an alkali metal chloride in the proportion of two parts alkali earth metal ch10- ride to one part alkali metal halide.

5. A molten bath for case-hardening metals comprising essentially not substantially over 1% sodium cyanide with a mixture of salts including calcium chloride and an alkali metal chloride, the calcium chloride forming at least 50% of the mixture.

6. A molten bath for case-hardening metals comprising essentially not substantially over 1% sodium cyanide with a mixture of salts including calcium chloride and an alkali metal chloride, in the proportion of two parts calcium chloride to one part alkali metal chloride.

7. A molten bath for case hardening metals comprising essentially to 1% of sodium cyanide with a mixture of salts including calcium chloride and sodium chloride in the proportion of about two parts calcium chloride to one part sodium chloride.

8. A molten bath for case-hardening metals comprising essentially a mixture of salts including an alkali earth metal chloride and sodium chloride in the proportion of approximately 2 parts of alkali earth metal chloride to 1 part of sodium chloride, and a minor portion of sodium cyanide as a case-hardening agent.

ERNEST c. MOFFETT. 

